Cans

ABSTRACT

A can has a metal end and a side wall of a different metal. Self-supporting sheet material which is water-impervious and electrolytically inert with respect to the metal of the side wall isolates the end from the contents of the can and serves to provide electrolytic corrosion of the end. Where the end is a tear-off end, the sheet also serves to preserve the contents from contamination if the tear-off end is damaged.

United States Patent Hornsby et a]. 51 Mar. 21, 1972 [54] CANS v [56]References Cited [72] Inventors: John M. Hornsby, Oakham; William G.UNITED STATES PATENTS Wood, Melton, both of England 3,220,599 1 1/1965Fried et al ..220/54 1 Assigneer Petfoods Limited, Leicester, 3,241,7083/1966 Ronci ..-.220/53 icestershire, England Primary Examiner-WilliamT. Dixson, Jr. [22] Filed Dec- AttorneySrnith, Michael, Bradford andGardiner [21] App]. No.: 881,542

' [57] ABSTRACT [30] Foreign Application Priority Data A can has a metalend and a side wall of a different metal. Selfsupporting sheet materialwhich is water-impervious and elec- DCC. l2, Great Britain trolyticallyinert i respect to the metal of the i W8" lates the end from thecontents of the can and serves to pro- [52] US. Cl. ..206/46 F, 99/171C, 220/54 I Vida electrolytic corrosion of the where the end is a {can[51] f "B65d 17/2orB65d 85/72 off end, the sheet also serves to preservethe contents from [58] Field of Search ..206/46 R, 46 F; 220/53, 54;contamination if the teapoff end is damaged 99/171 R, 171 M, 171 C 5Claims, 6 Drawing Figures CANS The present invention relates toimprovements in cans, for example cans for containing sterilized food,and more particularly to means for isolating an end of the can from thecontents of the can.

In the case of a can having a tear-off end, such ends usually beingscored or otherwise deformed to facilitate opening of the end by tearingout an area thereof, it is preferred to make the tear-off end ofaluminum, which can readily be torn, but the remainder of the can of astronger and/or less expensive material, such as tinplate. However, inthe presence of salts or other electrolytes in the contents of the canthe aluminum end corrodes, because an electric cell is set up betweenthe different metals, with the result that the canned product has anundesirably short shelf life The rate of corrosion can be diminished byreducing the concentration of salts in the contents but this is oftenundesirable, as for example in the case of canned foods, where the saltsare necessary nutritional ingredients.

The use of a tearable material for the ends of such cans and the scoringalso makes such cans more vulnerable to accidental damage.

The present invention enables the difficulties which are encountered inthe use of such cans to be overcome.

According to the invention, there is provided a can having a metal endand a side wall of a metal different from the metal of the end, in whichthe end is isolated from the contents of the can by a barrier ofself-supporting sheet material which is water-impervious andelectrolytically inert with respect to the metal of the side wall.

Where the said end is adapted to be opened by progressively tearing outan area thereof the sheet material can serve to preserve the contentsfrom contamination, for example contamination by entry of bacteriafollowing mechanical damage to the end.

In the case of cans which are subjected to heat treatment before and/orafter sealing the sheet material should be stable at the temperature ofthe heat treatment.

Examples of suitable sheet materials include thin tin foil cellulosefilm and films of laminates of thermoplastics materials, such aspolyethylene, polypropylene, polyamide and polyester.

Thus when a tinplate can body has a tear-off end of aluminum anundesirable rate of corrosion is avoided by the use of the sheetmaterials mentioned above. Where, on the other hand, an end is oftinplate, and the remainder of the can of aluminum, sheet material otherthan tinfoil should be used, for example aluminum foil, or the plasticsmaterials mentioned above.

It has proved difficult to provide a tear-off can end of tinplate owingto high tear strength of this material. The invention, by providing aninner sealing membrane, makes it possible to perforate a tinplate canend in order to render it more readily tearable, without loss of thepossibility of maintaining the sterility of the contents of the can. Theperforated end still plays an important protective role againstmechanical damage, for example during processing or subsequent handling,storage and transport, and pennits the use of readily tearable foils orfilms as the inner membrane.

The thermoplastics films mentioned, while imperforate, may exhibit asmall degree of porosity to gases, e.g., water vapor, but areimpermeable to micro-organisms, and thus serve to preserve the contentsof the can from bacterial contamination.

The present invention will now be more fully described with the aid ofexamples illustrated in the accompanying drawings in which:

FIGS. 1 and 2 illustrate steps in making a can according to theinvention and show a cross section through an end edge of a can inaccordance with the invention before and after sealing, respectively,

FIG. 3 shows in perspective a can in accordance with the invention,

FIG. 4 shows the can of FIG. 3 partly opened by tearing the end,

FIG. 5 shows in perspective an alternative form of a can in accordancewith the invention, and

FIG. 6 shows the can of FIG. 5 partly opened by tearing the end.

Conventional can-making techniques, only slightly modified, can be usedto produce the cans described herein.

Referring to FIG. 1, an aluminum can end 1 is shown placed over themouth of a tinplate can side wall 2. A layer 3 of a sealing compound,usually an organic solventor water-based composition, is applied to theperiphery of the underside of the end 1, as in conventional can-makingtechniques. A piece of polyester film 4 is placed on the underside ofthe end 1 and adheres to the sealing compound layer 3. Optionally, afurther layer 5 of the conventional sealing compound is applied to theperiphery of the underside of the film 4 to provide a good seal when theedges of the end 1 and the wall 2 are rolled and crimped together asshown in FIG. 2, in the usual sealing operation. In the sealingoperation, the edge of the film 4 becomes trapped between the edges ofthe end 1 and the wall 2. The film 4 serves to isolate the end I fromthe contents 6 of the can.

The can end 1 is scored along a line 7 around its periphery to provide aline of weakness along which the end 1 can be torn. The end 1 is alsoprovided with a circumferential groove 8, between its peripheral edgeand the score line 7, which serves to space the film 4 from underside ofthe can end 1 near its periphery to avoid the risk of the film 4 beingpunctured by the sharp edge of the end 1 if torn along the score line 7as a result of accidental damage.

The cans shown in FIGS. 3 to 6 have aluminum tear-off ends 1, with sidewalls 2 and plain ends (not visible) of tinplate, and are produced bythe method described above. The tear-off ends 1 are provided withring-pull finger grips 9 including a portion having a circular aperturetherein, through which protrudes a circular raised portion 10 of thealuminum can end 1 having its head riveted so as to form acircumferential shoulder securing the finger grip 9 and the can end 1together.

The can ends 1 are scored along lines 7 to facilitate tearing when thefinger grips 9 are pulled.

In the case of the can shown in FIGS. 3 and 4, the score line 7 definesa spiral-sided area which can be progressively torn out, commencingaround the raised and rivetted portion 10 of the can end 1. The scoreline 7 continues in a circle along the edge of the end 1, enabling acircular aperture to be made in the end 1 by tearing.

In the case of the can shown in FIGS. 5 and 6 the score line 7 proceedsin a circle along the edge of the end 1, enabling a circular area to betorn out, commencing at the region nearest the raised and rivetedportion 10 of the can end 1.

Each of the cans has polyester film 4 isolating the end 1 from thecontents of the can. The polyester film 4 can be readily torn to giveaccess to the contents.

In making the cans any impact adhesive or heat treatment may be used tobond the periphery of the piece of sheet material to the periphery ofthe can end instead of the usual sealing compound.

Instead of placing the sheet material on the can end, the sheet materialcan be placed over the mouth of the can before sealing.

What is claimed is:

1. A can comprising: a tubular metal side wall having first and secondends; first and second closure means closing respectively said first andsecond ends; material contained in said can enclosed by said side walland said first and second closure means; said first closure meansincluding an imperforate readily tearable member of a metal differentfrom that of said side wall and provided with means defining in saidmetal member a line of tear, and a barrier of self-supporting sheetmaterial which is water-impervious and inert to said contained materialand electrolytically inert with respect to the metal of said side wallin the presence of said contained minum.

3. A can as claimed in claim 1 wherein said sheet material is a film ofthermoplastics material.

4. A can as claimed in claim 2 wherein said sheet material is tinfoil.

5. A can as claimed in claim 1 wherein said member is provided withmeans for tearing from said member a portion thereof defined by saidline of tear.

1. A can comprising: a tubular metal side wall having first and second ends; first and second closure means closing respectively said first and second ends; material contained in said can enclosed by said side wall and said first and second closure means; said first closure means including an imperforate readily tearable member of a metal different from that of said side wall and provided with means defining in said metal member a line of tear, and a barrier of self-supporting sheet material which is water-impervious and inert to said contained material and electrolytically inert with respect to the metal of said side wall in the presence of said contained material; said barrier being disposed inwardly of said metal member, and means maintaining said barrier in spaced relation with respect to said metal member, at least in the area thereof bearing said line-oftear-defining means, to protect said barrier sheet against rupture by said tear-line-defining means, said barrier sheet isolating said metal member from said contained material, whereby electrolytic reaction between said side wall and said metal member is prevented.
 2. A can as claimed in claim 1 wherein said side wall is tinplate and said metal member of said first closure means is aluminum.
 3. A can as claimed in claim 1 wherein said sheet material is a film of thermoplastics material.
 4. A can as claimed in claim 2 wherein said sheet material is tinfoil.
 5. A can as claimed in claim 1 wherein said member is provided with means for tearing from said member a portion thereof defined by said line of tear. 